1. Field of the Invention
The present invention relates to a corrugated synthetic resin pipe which is to be buried in the ground or laid inside and outside a building on the ground or outdoors under a bridge, an elevated road, or the like, and which is used mainly for insertion of a cable, therethrough, such as an electric cable, a telephone cable, an optical cable, etc., the cable is protected by the pipe.
2. Background Art
Heretofore, generally, synthetic resin pipes each having a pipe wall shaped like an annularly or helically corrugated configuration are known widely. The pipes of this type have been already used as water pipes or sewage pipes. Further, the pipes of this type have begun to be used widely also as pipes for protecting cables such as telephone cables, etc. In any case of the conventional synthetic resin pipe whether the pipe is an annularly corrugated one or a helically corrugated one, all over the full length of the pipe has a substantially circular cross-section taken along a radial direction of the pipe and also has an corrugated cross section taken along the longitudinal direction of the pipe (hereinafter simply refering a circular-unevenly shape).
Because the conventional synthetic resin pipe is corrugate-shaped all over the full length of the pipe as described above, the pipe is apt to rotate circumferentially with poor stability when the pipe is to be laid. Accordingly, when a plurality of conventional pipes are to be laid in parallel with each other, the pipes are hardly kept parallel. Particularly when the conventional pipes are to be buried in the ground, earth and sand enter between the pipes so that the pipes move in a radial direction thereof. Accordingly, there is a problem that the straightness of pipe layout is apt to be disturbed. If predetermined straight pipe layout cannot be achieved, water stream resistance in the pipes increases more than that is required in the case where the pipes are used as water pipes or sewage pipes. If predetermined straight pipe layout cannot be achieved, frictional resistance in the work of inserting cables, or the like, into the pipes increases more than that is required in the case where the pipes are used as cable protective pipes. Accordingly, there is a problem that workability is lowered.
Therefore, a Japanese Patent Unexamined Publication No. Hei. 8-21933 had paid attention to the problems in such conventional circular corrugated pipes and had previously developed a synthetic resin pipe P as a pipe having a novel structure to solve these problems in the conventional pipes. That is, as shown in FIGS. 16 and 17, the publication discloses that the synthetic resin pipe P has a pipe wall 1 formed by alternatively arranging sectionally square wall portions 2 and sectionally circular wall portions 3 in the longitudinal direction of the pipe, in such a manner that the presence of the sectionally square wall portions 2 prevents the pipe from rotating in a circumferential direction thereof or moving in a radial direction thereof recklessly.
On the other hand, the previously developed pipe P was designed such that a sectionally circular wall portion formed as a portion between adjacent sectionally square wall portions was shaped in a simple cylinder. Accordingly, when the circular wall portions were used for connecting ends of pipes to each other, it was difficult to connect the pipe ends to each other watertightly. Further, even in the case where pull-apart external force acted in the longitudinal direction of the pipes, it was difficult to achieve secure connection to keep the pipes watertight against the external force. On the other hand, when the sectionally square wall portions were used for connecting ends of pipes, the joint portion became large so that the joint portion was projected largely over the outer circumference of the pipes.
Accordingly, it was difficult to perform parallel pipe laying out, stack pipe layout, or serial pipe layout in an ordinary state. In that situation, it could not be said that such connection was desirable.